Casement windows are those in which the window is opened by pivoting the sash about one edge of the sash in contrast to double hung windows, for example, in which the window is opened by a sliding of the sash along a track.
In one type of casement window, the bottom edge of the sash is supported on a long lever having one end pivotally mounted to a slider that may move left and right along a track. The track is attached to the sill (or opposing lintel) of the opening of the window. A second, short lever pivots about another fixed point on the track and is attached to the center of the first lever by a pivot. Opening of the sash causes a sliding inward of the effective axis about which the sash swings, the "sash axis" toward the center of the window opening, providing improved accessibility to both sides of the window.
One of the problems with casement windows is "sash sag" which can cause the lower swinging edge of the sash to strike the sill when the window is returned to the closed position. Sash sag may be caused by poor installation of the window unit causing the window opening into which the sash fits to no longer be square, or by poor hinge positioning by the window manufacturer.
One method of correcting for sash sag involves repositioning the hinges. U.S. Pat. No. 4,790,106 assigned to the same assignee as the present invention and hereby incorporated by reference, describes a cam system for moving the entire system track and hinge assembly of the casement window, left or right with respect to the window opening thereby aligning the sash axis with the window opening.
Alternatively, the need to move the entire track and hinge assembly with respect to the window opening may be avoided by changing the position of the pivot point at which the short lever (described above) is attached to the track. For a given angle of opening of the sash, a change in this pivot point will change the location of the slider on the track. Changing the location of the slider on the track changes the point about which the sash pivots allowing correction of the sash axis.
Cam systems for changing the pivot point of the short arm is described in U.S. Pat. Nos. 5,074,075 and 5,152,102 also assigned to the assignee of the present invention and incorporated by reference.
The pivot point attaching the short arm to the track must be rugged and capable of withstanding the forces generated by wind and in opening and closing the window. These forces are applied at varying angles and opposite directions depending on whether the window is being opened or closed.
Because the movement of pivot point to correct sash sag is small, an adjustable pivot point must be designed to resist slippage with use of the window. Nevertheless, the mechanism for adjusting the pivot point must be compact to fit within the normal width of the track and to be compatible with standard window openings. Further, it is desirable that the pivot point be readily adjusted without the need for special tools or significant disassembly of the window or hinge and track assembly. It is difficult to meet these requirements as well as to produce a mechanism that is durable, readily manufactured, and reasonable in cost.